Filter for removing oxides of nitrogen from tobacco smoke



United States Patent 3,390,688 FILTER FOR REMOVING OXIDES 0F NITRGGEN FROM TOBACCO SMOKE George P. Touey and Bobby J. Sublett, Kingsport, Tenn, assignors to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey No Drawing. Filed Mar. 13, 1967, Ser. No. 622,411 7 Claims. (Cl. 131266) ABSTRACT OF THE DISCLQSURE Filter elements containing a salt of chlorous acid which will react with and neutralize a high percentage of the oxides of nitrogen in tobacco smoke. The salt is impregnated into basic granular material, having a pH greater than S.

Tobacco smoke, as is well known, consists of a gaseous or vapor phase in which are suspended liquid or semiliquid droplets and certain solid particles. It is also known that various compounds and materials that exist in these gaseous, liquid and solid phases of the tobacco smoke contribute nothing beneficial to the pleasant taste or aroma of the smoke. Thus much effort has been expended in developing suitable methods and devices for removing these deleterious compounds and materials from tobacco smoke without at the same time affecting the pleasant flavor and aroma of the smoke. This concerted effort led to the development of the standard commercial cigarette filter which normally consists of a bundle of cellulose acetate fibers or convoluted creped paper formed into a cylindrical plug. Such filters are designed to and do remove varying proportions of the droplets and solid particles from tobacco smoke thereby greatly reducing the amount of undesirable materials reaching the smokers mouth. This filtering action is accomplished by a combination of diffusional, impactive, and direct collision of the droplets with the filter material. U-pon collision the droplets are retained in the filter mainly by the surface attraction between the extremely small articles and the relatively large filter material.

However, these plug type filters per se generally are unable to remove many of the noxious vaporized components from the smoke stream by the processes of physical and chemical adsorption. Certain of these gaseous components are especially toxic and adversely affect the human tissues with which they come into contact. The various oxides of nitrogen and in particular nitric oxide and nitrogen dioxide constitute one group of these undesirable gases to be found in the smoke of burning tobacco. This specific group of gaseous component of tobacco smoke merits special attention, however, since some are known to be especially toxic substances.

In attempts to improve the gaseous removal properties of tobacco smoke filters various additives to known filtering material, and certain new filtering materials, have been proposed and tried. Among the materials proposed for use in or with the tobacco smoke filter was a number of well-known adsorbents such as activated charcoal, alumina, natural and synthetic clay, and silica gels. Such adsorbent-containing tobacco smoke filters are effective to some extent in removing certain deleterious gases from the vapor phase of cigarette smoke, but their use has some definite disadvantages. For example, such adsorbent additive indiscriminately remove from the tobacco 3,396,688 Patented July 2, 1968 ice smoke not only certain obnoxious or toxic components, but many other components as well which are necessary for maintaining the desired fiavor and aroma of the smoke. In the case of activated carbon, which at the present time is the most commonly used adsorbent type additive for cigarette filters, the removal of these flavoring agents imparts an undesirable taste to the smoke that is commonly referred to as the carbon taste. Also, since the adsorption of vapors by these materials is based on physical phenomena, which are in turn dependent upon temperature and pressure, many of the adsorbed vapors including those that are deleterious are later released in concentrated quantities as the burning zone of the cigarette approaches the filter during the smoking of the cigarette. Furthermore, activated carbon and the mineral adsorbents are essentially ineffective for removing such dilficultly condensed gases as nitric oxide or nitrogen dioxide under the conditions imposed during the smoking of a filter cigarette.

Therefore, it is readily apparent that an improvement in the tobacco smoke filter art which would permit the substantial reduction or complete elimination of the oxides of nitrogen from tobacco smoke without at the same time adversely affecting the flavor and aroma of the smoke would represent a substantial stride forward. Ideally this improvement should use a material and/or method that is inexpensive, reliable and commercially available. Furthermore, the filter should be capable of selectively removing only deleterious vapors found in tobacco smoke, and the vapors should be removed permanently by a chemical reaction so that they will not be eluted from the filter toward the end of the smoking cycle. The process whereby the filter is produced must also be compatible with existing manufacturing equipment and capable of being performed at the high speeds demanded by industry.

According to the present invention a convenient and effective method has been found by which a tobacco smoke filter can be constructed for the selective removal of the oxides of nitrogen from tobacco smoke by a chemical reaction. This method consists of coating, dusting, or otherwise dispersing selected additives, which have been treated with a specific group of inorganic oxidizing agents, onto the filtering material from which the tobacco smoke filter element is formed. The oxides of nitrogen are converted chemically to an inert material upon their contact with the additives in the filter and this inert material remains in the filter. Therefore, the oxides of nitrogen are prevented from reaching the smokers mouth.

An object of this invention is to provide a new and improved tobacco smoke filter unit.

Another object of this invention is to disclose a chemi cal additive for tobacco smoke filters which will substantially eliminate certain specific deleterious vapors or gases found in tobacco smoke.

Yet another object of this invention is to disclose a coated or impregnated granular additive for use With a tobacco smoke filter which will chemically reduce the concentration of certain specific deleterious vapors or gases, such as the oxides of nitrogen, from the tobacco smoke passing through the filter.

Still another object of this invention is to disclose a new tobacco smoke filter tow, and a method of manufacturing the same, which contains salts of chlorous acid which are capable of chemically reacting with the oxides of nitrogen found in tobacco smoke to a harmless material.

A further object of this invention is to describe a cigarette filter having certain basic water-insoluble powders impregnated with water-soluble salts of chlorous acid therein for selectively removing nitrogen oxide vapors from tobacco smoke by a chemical technique.

A still further object of this invention is to describe a method and process of manufacturing a cigarette filter from a cellulose acetate tow which contains chlorous acid salts capable of removing nitrogen oxides from tobacco smoke.

Yet another object of this invention is to describe a dual-type cigarette filter composed of two separate segments of fibrous filter materials, one segment having dispersed throughout its fibers certain basic water-insoluble powders impregnated with water-soluble salts of chlorous acid for selectively removing oxides of nitrogen from the smoke.

An additional object is to describe a three component type cigarette filter two components consisting of plugs of paper, cellulose acetate, or some other fibrous filter material and the third component consisting of loose granules of chlorite salt impregnated or coated powder positioned between the two fibrous components and coaxially aligned with them.

These and further objects and advantages of this invention will be more apparent upon reference to the accompanying specification, specific working examples, and claims.

As set out hereinabove, this invention involves the use of certain Water-soluble salts of chlorous acid in tobacco smoke filters for selectively removing oxides of nitrogen from tobacco smoke. The specific oxidizing agents which have been found to be particularly adapted for removing oxides of nitrogen from tobacco smoke are the watersoluble chlorous acid (HCIO salts of the monoor divalent metals selected from the group consisting of potassium (K sodium (Na magnesium (Mg++), or calcium (Ca++).

Since the salts of chlorous acid act through physical contact to chemically react with the nitrogen oxide vapors, it is very important that as much surface area of the salts be exposed for contact with the oxide vapors as possible. For this reason it is desirable that the chlorous acid salts be coated on a surface such as granular particles which has relatively large surface area. However, it has been found that only those granular materials which have a pH greater than 8 when dropped in water will give the desired results. The reason for this is not yet fully understood but it is believed to involve the oxidation of the oxides of nitrogen to nitrous or nitric acids and the subsequent neutralization of these acids to nonvolatile salts within the filter due to the basicity of the chlorite salt impregnated material. This theory would seem to be further verified by the fact that basic materials used alone on cigarete filters do not effectively remove oxides of nitrogen from cigarette smoke since they do not convert them to neutralizable acids.

There are several different inorganic basic carrier materials that can be used. Specifically, it has been found that basic inorganic, water-insoluble powdered carriers such as the naturally occurring clays which include meerschaum, fullers earth, perlite or the like can be coated with the oxidizing agent (chlorous acid salts). It has also been found that the use of other inorganic basic carrier materials such as aluminum oxide, magnesium oxide, calcium carbonate, magnesium carbonate and the like also give excellent results. In fact, a nearly perfect basic inorganic water-insoluble carrier powder for the water-soluble chlorites is aluminum oxide which is either basic as manufactured or has been made basic by treatment with alkali metal hydroxides or carbonates. Also, it may be a neutral powder which has been coated with a basic material before or after the treatment with the chlorite salt providing the powder is inert to the chlorite salt.

The chlorite salts contemplated by this invention can be incorporated into or added onto the basic inorganic material by any suitable method. For example, the chlorite salts may be dissolved in a suitable solvent, such as water, and then applied to the carrier material by spraying, soaking, sprinkling or the like after which the solvent is driven off as a vapor leaving the additive thoroughly incorporated within and/0r over the material. The amount of oxidizing agent (sodium chlorite salts) which can be used is from about 0.5 to 50 percent based on the weight of the additive (granular or powder) with the preferred range being from about 5 to 20 percent.

After the chlorite salt impregnated basic material has been prepared it can either be added to or formed into a tobacco smoke filter element. For example, basic powders that have been impregnated with at least one chlorite salt can be dusted or otherwise added to a filter unit by any of the many known methods for incorporating solid particles into such filters. This results in a fibrous filter wherein the additive powder is co-rningled with the fibers. The chlorite salt containing additives can also be utilized by themselves as one element of a dual or multicomponent filter. This can be accomplished by using the additive as the middle portion of the filter in much the same manner as carbon is now employed in certain commercial tobacco smoke filters. The front and back portions of the filter can be constructed from any suitable filtering or holding material such as, for example, cellulose acetate tow.

It should be understood, however, that these examples of the type of filter materials that can be used, the method of applying the chlorite salts to the filters, and the type of filters thus formed are given for purposes of illustration only. Clearly, numerous filter materials such as paper, cotton, cellulose acetate fibers, polyolefin, and polyester fibers or the like could be readily treated with the chlorite salts of this invention after which they could then be formed into any number of different type filter elements. Thus, the only essential property which the filter must have is that it be so constructed that the etfuiding stream of tobacco smoke will come into contact with the chlorite salts which converts the oxides of nitrogen from nitric oxide or nitrogen dioxide to nitrite and nitrate, respectively. Since these species form a relatively nonvolatile salt with the base, the products of the reactions remain chemically bound to the additive within the filter.

Regardless of the method of incorporating the chlorite containing powders of this invention into a filter for cigarettes, the amount of powder in the filter must be such that at least 5 mg. of chlorite salt are present to make contact with the smoke. Within practical limits the concentration of chlorite salt on the treated and dried additive should not be less than 3% and preferably it should be between 10 and 30%. For example, if the carrier powder contains say only 2% of the salt at least 250 mg. of the powder would have to be incorporated into the filter to obtain only the minimum requirements of 5 mg. of chlorite salt. On the other hand, at the 10% concentration level for the chlorite salt only 50 mg. of powder would be needed to give the minimum 5 mg. of chlorite salt in the filter. In other words it is desirable from a practical standpoint to keep the total amount of additive at a maximum of 200 mg. and this is easily accomplished when the percentage of chlorite salt in the filter additive is between 10 and 30%.

A further understanding of the invention will be had from a consideration of the following examples which are set forth to both illustrate the invention in general and to specifically illustrate certain preferred embodiments that can be used in actual commercial practice.

EXAMPLE I A 10 in. length of 8 denier/filament crimped cellulose acetate filter tow which had 8,000 filaments and weighed approximately 20 grams was spread out to a width of inches. Glyceryl triacetate in the amount of 8% by weight of the tow was applied to the tow by spraying. Two and one-half (2.5) grams of aluminum oxide granules sold under the trade name Alumina and having a mesh size of 50, which had 10% by weight sodium chlorite coated on its surface from a water solution, was distributed throughout the tow from a shaker. The tow was then recompacted and wrapped with a paper tape to form a rod. The rods were then cut into 20 mm. segments. The 20 mm. segments were attached to king-size cigarettes by means of a cellophane tape. The cigarettes were smoked with an automatic smoking device. The vapors which passed through their filters followed by a glass wool filter (Cambridge filter), which removed the particulate phase of the smoke, were collected in an evacuated gas sampling device. They were then analyzed for NO and N0 using a colorimetric method described by Saltzman (Anal. Chem. 26, pp. 1949-54, 1954). Similar filter cigarettes were smoked with the automatic smoking device, and this time the vapors which passed through the filters were collected and analyzed by gas chromatography according to the method described by A. H. Laurene et al. in Tobacco, 159, pp. 34-37, Nov. 27, 1964. The amounts of several of the components of the collected gas are listed in the Table 1. Also contained in the table are the amounts of these vapors collected from the smoke of similar cigarettes containing a 20 mm. cellulose acetate tip, and containing a cellulose acetate filter with 200 g. of alumina additive which had not been coated with sodium chlorite.

TAB LE 1 g. Found in Smoke from Cigarettes Containing Filters These results illustrate that only the filter containing the chlorite salt selectively removed the oxides of nitrogen but did not disrupt the concentration of other components in the gas phase of cigarette smoke.

EXAMPLE II A 170 mm. length of 3 denier/filament crimped cellulose acetate filter tow which had 20,000 filaments and weighed approximately 1 g. was spread out to a width of 15 inches. Then glyceryl triacetate was sprayed onto the tow in the amount of 8 percent. Then 1 g. of alumina (pH 9.2) which had 10% weight sodium chlorite coated on its surface was shaken on to the tow. The tow was recompacted and wrapped with a paper tape to form a filter rod with a circumference of mm. This circumference is equal to that of a standard domestic cigarette. The rod was allowed to stand until it became rigid. The rod was cut into 17 mm. segments which contained approximately 100 mg. of the coated alumina additive per segment. The 17 mm. filter segments were attached to king size cigarettes by means of a cellophane tape. The cigarettes were smoked with an automatic smoking device to a 30 mm. butt-length. The vapors which passed through the filter were collected and analyzed as described in Example I. The amounts of several of the components of the collected gas are listed in Table 2. Also shown in the table are the amounts of these vapors obtained from the smoke of (1) similar cigarettes containing a 17 mm. cellulose acetate filter, and (2) cigarettes having cellulose acetate filters containing alumina which had not been coated with sodium chlorite.

TABLE 2 g. Found in Smoke from Cigarettes Coutaining Filters Component Cellulose Cellulose Acetate Cellulose Acetate plus Alumina Acetate plus Filter plus Sodium Alumina Chlorite Acetaldehydc 800 800 800 Propionaldehyde. 40 40 40 Methanol 120 120 Methyl Ethyl Keton 75 75 75 Isopreue 600 600 600 Nitric Oxide and Nitrogen Dioxide 170 20 170 EXAMPLE III A 170 mm. length of 3 denier/filament crimped cellulose acetate filter tow which had 20,000 filaments and weighed approximately 1.5 g. was spread out to a width of 15 inches. Then glyceryl triacetate was sprayed onto the tow in the amount of 8% by weight. One gram of 30 mesh meerschaum (sepiolite clay) granules (pH 9.8), which had been coated with 10% by weight sodium chlorite, was shaken on to the tow. The tow was then recompacted and wrapped with a paper tape to form a filter rod with a circumference of 25 mm. This circumference is equal to that of a standard domestic cigarette. The rod was then allowed to stand until it became rigid. The rod was cut into 20 mm. segments which contained approximately mg. of the coated meerschaum (sepiolite) additive on each 20 mm. segment. The 20 mm. filter segments were attached to king size cigarettes by means of a cellophane tape. The cigarettes were smoked with an automatic smoking device to a 30 mm. butt length. The vapors which passed through the filter were collected and analyzed as described in Example I. The amounts of several of the components of the collected gas are listed in Table 3. Also shown in the table are the amounts of these vapors obtained from the smoke of (1) similar cigarettes having plain 20 mm. cellulose acetate filters, and (2) cigarettes having cellulose acetate filters containing meerschaum which had not been coated with sodium chlorite.

A crimped cellulose acetate tow filtered of 8 denier per filament and containing 5000 filaments 'was spread out to a width of 12 inches. While in this spread out condition the tow was dusted with calcium carbonate powder which had previously been soaked in a 30% solution of calcium chlorite, filtered and dried so that it contained 15% of the chlorite salt. The dusted tow containing 1 g. (1000 mg.) of the powder for every 100 mm. of its length was compacted and drawn through a device which paper wrapped it and cut it into the form of cylindrical filtered rods with a circumference equal to that of acigarette. Due to the relatively heavy fibers and the powder these rods were firm and therefore did not need a hardening agent such as glycerol triacetate. Several of the rods were cut into 10 mm. filter segments and these were attached to cigarettes which wereknown to produce 150-170 mg. of NO-NO when automatically smoked (50 mm. of tobacco) with a 35 ml. puff of Zseconds duration at the rate of 1 puff per minute. These filter cigarettes, when automatically smoked (50 mm. of tobacco) as designated above, yielded only 60-70 mg. of NO-NO indicating that the filters removed about 60% of the oxides of nitrogen from the smoke.

EXAMPLE V Two other sections of an 8 denier per filament tow made in the manner described in Example IV were treated with chlorite containing powders and processed into 10 mm. filters in exactly the same manner as described in Example IV. In one case the filters contained 100 mg. of magnesium carbonate powder coated with potassium chlorite and in the other they contained 80 mg. of a magnesium silicate type of clay containing potassium chlorite. When the filters were attached to the standard cigarettes of Example IV it was observed that those containing the magnesium chlorite treated powder removed 50% of the oxides of nitrogen while those containing the potassium chlorite treated powder removed 69% of the oxides of nitrogen.

From the foregoing description it is readily apparent that the salts of chloric acid containing tobacco smoke filter of this invention offers a definite detoxicating advantage over those filters previously known and used in the cigarette industry. For example, not only is the additive a highly selective one which is capable of removing substantial amounts of the oxides of nitrogen found in tobacco smoke as it moves through the interstices of the filters, but the nitrogen oxides removed by contacting the oxidizing additive is neutralized to an inactive and harmless by-product which cannot later be eluted from the filter. Furthermore, the fact that the additive does not remove tobacco smoke vapors in general, but rather selectively removes the highly volatile gases of nitrogen oxides is extremely important. Also, this additive selectively removes these deleterious components from the vapor phase of the tobacco smoke without in any way decreasing the capacity of the filter for removing particular matter (tar) from the smoke.

What is claimed and desired to be secured by the United States Letters Patent is:

1. As a new article of manufacture, a tobacco smoke filter element containing an additive of a basic granular material, having a pH greater than 8, that has been treated with a salt of chlorous acid selected from the group consisting of sodium chlorite, potassium chlorite, calcium chlorite and magnesium chlorite wherein said treated additive will react with and neutralize a major proportion of the oxides of nitrogen in the tobacco smoke passing through said filter element.

2. An intermediate for use in the manufacture of a tobacco smoke filter element comprising a basic granular material having a pH greater than 8 that has been treated with a salt of chlorous acid selected from the group consisting of sodium chlorite, potassium chlorite, calcium chlorite and magnesium chlorite, wherein said intermediate will react with and neutralize oxides of nitrogen in the tobacco smoke passing through said filter element.

3. An intermediate according to claim 2 wherein the salt of chlorous acid is coated on said basic material.

4. An intermediate according to claim 3 wherein said basic material is a neutral material which has been coated with a basic material.

5. A cigarette filter material consisting of a fibrous material carrying on its fibrous surfaces a basic granular material, having a pH greater than 8 said granular material having been treated with a solution of an oxidizing material, said oxidizing material being selected from the group consisting of sodium chlorite, potassium chlorite, calcium chlorite, and magnesium chlorite.

6. A erimped cellulose acetate tow filter material carrying on its fibrous surfaces granules of a basic aluminum oxide having a pH greater than 8, the aluminum oxide having been impregnated with from about 12()% of a material selected from the group consisting of sodium chlorite and potassium chlorite.

7. A three component filter for cigarettes wherein two components consist of fibrous materials and the third consists of basic granules having a pH greater than 8, containing from about 110% of a material selected from the group consisting of sodium chlorite and potassium chlorite, the granules being contained loosely in a compartment between the fibrous filter plugs.

References Cited UNITED STATES PATENTS 1,519,470 12/1924 Wilson et al. 131-267 2,181,614 11/1939 Striefling 131-10.9 2,739,598 3/1956 Eirich 13110.9 3,032,445 5/1962 Hamon 13110.9 3,149,907 9/1964 Karwat 232 3,251,365 5/1966 Keith et al. 131-265 X 3,347,245 10/1967 Hawkins 13l266 X FOREIGN PATENTS 1,110,463 10/1955 France.

834,854 5/1960 Great Britain.

SAMUEL KOREN, Primary Examiner.

DENNIS I. DONOHUE, Assistant Examiner. 

